1. Technical Field
The invention relates to the field of packet cellular wireless networks and, more particularly, to an algorithm which improves upon the flexibility and efficiency of packet delivery to users of cellular services.
2. Description of the Related Arts
Cellular wireless data networks have inherent sources of inequality and unfairness since the channel conditions are not uniform for all users. Clearly, some mobile cellular wireless users, depending on various factors, experience better service quality at different times during a call, for example, when the user is mobile or due to atmospheric or topographic considerations in the path from mobile station to base station. To support efficient data access in cellular wireless networks where vast amounts of data may be downloaded to a user, for example, of a pocket personal computer, network operators will have to decide on how to optimize the performance of users with different channel qualities and at the same time maintain a certain degree of fairness. Packet scheduling, which assigns radio resources to mobile stations, plays a critical role in this process.
There have been a number of scheduling algorithms proposed for wireless networks. In general, these algorithms defer sending packets for a mobile station during error bursts, and resume transmission only when the link quality improves to an acceptable level. Some of them also supplement the mobile station with additional bandwidth for the time period that it was skipped to achieve certain fairness.
There are two closely related problems that are not addressed in the previous work. First, users may deliver different amounts of data using the same amount of radio resource, for example in systems with link adaptation. Since it can never be predicted exactly whether a packet will be transmitted successfully in cellular systems, the network will typically deliver the packet so long as its error probability is lower than a certain threshold. So some packets may end up having errors and have to be discarded. Moreover, because wireless users may have different channel qualities, the packet error rates can vary significantly from user to user. As a result, users may deliver different amounts of data using the same amount of channel resource. This is particularly important in wide-area cellular environments, where packet errors are much more common and harder to predict. Secondly, the focus of the previous work has been on providing the kind of fairness such that when averaging over some time period, users can receive their data rate guarantees, so long as their channel conditions permit. Although this type of fairness is necessary when stringent delay and rate requirements are specified in a service level agreement with the user, most of the best-effort data applications, such as web browsing and email, are much more flexible in terms of rate and delay. Loosened quality of service (QoS) requirements make it very compelling for network operators to seek alternative scheduling schemes that can improve system efficiency.